The lines between our features become blurred as our software grows. There's bound to be at least some overlap, and that can be a good thing. If there wasn't at least a little overlap, users would have a tough time transitioning from one area of our UI to another. This becomes a problem when we reach a feature threshold where there're multiple overlapping layers that just keep overlapping. It's a self-propagating problem that get's worse with every new feature added, till it is addressed.
Two potential causes of this problem include parts of our application that grow irrelevant over time, and instead of being retired, they sit around and get in the way. Customer demand plays a big part in this scaling influence because it determines the future direction of the product. This should also give us an indication of what's in place now, that either needs to change in order to meet demand, or needs to go away in the near future.